1. Field of the Invention
The present invention relates to a motor control apparatus.
Priority is claimed on Japanese Patent Application No. 2007-114047, filed Apr. 24, 2007, the content of which is incorporated herein by reference.
2. Description of Related Art
There has been a desire for higher frequency motors in order to increase motor output while decreasing motor size.
By increasing the pairs of poles of a motor, for example, there is a decrease in the circumferential width of the teeth of the stator and an accompanying reduction in the width of the back yoke that supports the teeth. As a result, the control frequency of the motor becomes higher accompanying the reduction in motor size. In addition, the torque that a motor is capable of outputting increases and decreases in accordance with motor size. Thus, by increasing the revolutions that can be achieved, it is possible to increase output (i.e., product of torque and revolutions) while decreasing motor size.
However, when operating a motor at high frequency, the stability of the control system deteriorates due to errors in the detection of the rotation phase and higher harmonic components in the electrical current passing through the motor. There are therefore conventionally known control apparatuses for correcting detection errors of rotation phase or suppressing the higher harmonic components included in the electrical current passing through the motor (see Japanese Unexamined Patent Application, First Publication No. 9-308300 and Japanese Unexamined Patent Application, First Publication No. 2001-298992, for example).
In the motors according to the aforementioned conventional technology, the induction voltage of the motor includes various higher harmonic waves, and the current flowing through the motor includes higher harmonic components. For this reason, the current values sampled at each control period during current feedback control and other such sequential control processing vary at a period corresponding to the least common multiple of the control period and the period of the higher harmonic components. As a result, when the control period approaches the period of the higher harmonic components, sub-harmonic variation and regular off-set occurs, leading to a deterioration in the control system.
Due to errors of the detection system or the like, a resolver or other such angle sensor, which outputs a pulse in accordance with the rotation angle of the motor, will generates an error of a 360° (edeg) or 180° (edeg) period in terms of electrical angle. Thus, when the control period approaches the 360° (edeg) period in terms of electrical angle, sub-harmonic variation and regular off-set occur, problematically leading to a deterioration in the control system.
In a resolver and R/D (resolver/digital) converter, for example, feedback control is executed so that θ=Φ for the signal shown by the following equation (1), where E sin ωt is the exciting voltage, K is a voltage transformation ratio, θ is the rotation angle of the resolver, and Φ is the output counter value.
Here, when a suitable off-set α is applied to the detection signal of the resolver, then, as shown by the following equations (2) and (3), an error (θ−Φ) of a 360° (edeg) period in terms of electrical angle is generated.
Moreover, when a reasonable deviation β is generated in the amplitude of the detected signal of the resolver, then, as shown by the following equations (4) through (6), an error (θ−Φ) of a 180° (edeg) period in terms of electrical angle is generated.
                                                        KE              ·              sin                        ⁢                                                  ⁢            ω            ⁢                                                  ⁢                          t              ·              sin                        ⁢                                                  ⁢                          θ              ·              cos                        ⁢                                                  ⁢            Φ                    -                                    KE              ·              sin                        ⁢                                                  ⁢            ω            ⁢                                                  ⁢                          t              ·              cos                        ⁢                                                  ⁢                          θ              ·              sin                        ⁢                                                  ⁢            Φ                          =                              KE            ·            sin                    ⁢                                          ⁢          ω          ⁢                                          ⁢                      t            ·            sin                    ⁢                                          ⁢                      (                          θ              -              Φ                        )                                              [                  Equation          ⁢                                          ⁢          1                ]                                                                                    (                                                                            KE                      ·                      sin                                        ⁢                                                                                  ⁢                    ω                    ⁢                                                                                  ⁢                    t                                    +                  α                                )                            ·              sin                        ⁢                                                  ⁢                          θ              ·              cos                        ⁢                                                  ⁢            Φ                    -                                    KE              ·              sin                        ⁢                                                  ⁢            ω            ⁢                                                  ⁢                          t              ·              cos                        ⁢                                                  ⁢                          θ              ·              sin                        ⁢                                                  ⁢            Φ                          =                                                            KE                ·                sin                            ⁢                                                          ⁢              ω              ⁢                                                          ⁢                              t                ·                sin                            ⁢                                                          ⁢                              (                                  θ                  -                  Φ                                )                                      +                                          α                ·                cos                            ⁢                                                          ⁢              Φ                                =          0                                    [                  Equation          ⁢                                          ⁢          2                ]                                          (                      θ            -            Φ                    )                ≈                                            -              α                        ·            cos                    ⁢                                          ⁢          Φ                                    [                  Equation          ⁢                                          ⁢          3                ]                                                                    (                              1                +                β                            )                        ⁢                          KE              ·              sin                        ⁢                                                  ⁢            ω            ⁢                                                  ⁢                          t              ·              sin                        ⁢                                                  ⁢                          θ              ·              cos                        ⁢                                                  ⁢            Φ                    -                                    KE              ·              sin                        ⁢                                                  ⁢            ω            ⁢                                                  ⁢                          t              ·              cos                        ⁢                                                  ⁢                          θ              ·              sin                        ⁢                                                  ⁢            Φ                          =                                            KE              ·              sin                        ⁢                                                  ⁢            ω            ⁢                                                  ⁢                          t              ·                              {                                                      sin                    ⁡                                          (                                              θ                        -                        Φ                                            )                                                        +                                      β                    ⁢                                                                                  ⁢                    sin                    ⁢                                                                                  ⁢                                          θ                      ·                      cos                                        ⁢                                                                                  ⁢                    Φ                                                  }                                              =                                                    KE                ·                sin                            ⁢                                                          ⁢              ω              ⁢                                                          ⁢                              t                ·                                  {                                                            sin                      ⁡                                              (                                                  θ                          -                          Φ                                                )                                                              +                                          β                      ⁢                                                                                                    sin                            ⁡                                                          (                                                              θ                                +                                Φ                                                            )                                                                                +                                                      sin                            ⁡                                                          (                                                              θ                                -                                Φ                                                            )                                                                                                      2                                                                              }                                                      =            0                                              [                  Equation          ⁢                                          ⁢          4                ]                                          sin          ⁡                      (                          θ              -              Φ                        )                          =                                            -                              β                                  2                  +                  β                                                      ⁢                          sin              ⁡                              (                                  θ                  +                  Φ                                )                                              =          0                                    [                  Equation          ⁢                                          ⁢          5                ]                                          θ          -          Φ                ≈                                            -                              β                                  2                  +                  β                                                      ·            sin                    ⁢                                          ⁢          2          ⁢          Φ                                    [                  Equation          ⁢                                          ⁢          6                ]            